The proposed research plan will focus on the relationship between mutations in the primary structure of hemoglobin and mechanisms regulating cation content and cell volume of human red cells. This proposal stems from our observation that CC cells (cells homozygous for hemoglobin C) possess a ouabain- bumetanide-resistant pathway for K transport that is pH and volume dependent and allows CC cells to regulate their volume upon swelling. The reduction of cation and water content described in CC cells takes place through this pathway. This suggests a possible role for the relatively positive charged hemoglobin C in the activation of a pathway involved in the control of cell volume. Specific aims include: 1) Further characterization of the pH and volume dependent K transport system of CC cells; 2) Testing the hypothesis that hemoglobin C is responsible for the activation of this pathway; 3) Investigation of cation transport properties of other relatively positive or negative charged hemoglobin variants; 4) Examination of the mechanisms involved in the control of cation and water content, and cell volume in cells homozygous (SS), and heterozygous (AS) for hemoglobin S, and SC cells, and their role in cell sickling. These studies should provide new information on the mechanism by which this pH and volume dependent pathway for K transport is activated in CC cells. In addition, these studies may also provide new insights into the role of hemoglobin-membrane interactions in the regulation of cation content and cell volume and possibly provide a new approach to the study of cation permeability changes induced by sickling.